Electro-deposition of copper from acidic baths



United States Patent 3,328,273 ELECTRO-DEPOSHTKQN OF COPPER FRUM ACHDHC BATH Hans-Gerhard Creutz, Wayne, Richard M. Stevenson,

Grosse Pointe Woods, and Edward A. Romanowski,

Troy, Mich, assignors to The Udylite Corporation,

Warren, Mich, a corporation of Delaware No Drawing. Filed Aug. 15, 1966, Ser. No. 572,201

Claims. (Cl. 204--52) This application is a continuation-in-part of our c0- pending application, Ser. No. 187,926 filed Apr. 16, 1962 which is now U.S. Patent No. 3,267,010.

This invention relates to the electrodeposition of copper from aqueous acidic baths, especially from copper sulfate and fiuoborate baths. More particularly it relates to the combined use of certain organic compounds in such baths to make possible bright, highly ductile, low stress, good leveling copper deposits.

While a rather large number of organic compounds have been previously proposed and used to decrease the grain size and increase the luster of copper deposits from acidic baths, nevertheless, much remains to be desired from the standpoint of obtaining lustrous leveling copper plate without striations and ribbing and without substantially decreasing the very high ductility of the copper plate.

In our copending application Ser. No. 187,926, we have described certain organic sulfide compounds containing at least one sulfonic group which when used in combination with certain bath soluble polyether compounds produce bright, ductile copper electrodeposits. The baths described therein have excellent brightness and ductility and are operable over a fairly wide current density range. While these baths have been adequate to meet the requirements of most commercial applications, very complex parts require that a plating bath have an extremely wide current range. Thus, there have been instances wherein the current density of the above described baths has not been sufficient to satisfactorily plate some extremely complicated articles and the plate has proved to be inadequate in the deeply recessed areas.

Another limitation with the baths described in our copending application is that the concentration of the sulfide component therein should be kept below about 0.04 gram per liter. At concentrations much above this level, there is a tendency to form harmful breakdown deposits on extended electrolysis which results in a reduced brightness, especially in the low current density areas.

An object of this invention is to provide copper plating baths from which are obtained bright, ductile copper deposits free of striations and ribbing. Another object is to provide plating baths from which such copper deposits are obtained over a wide current density range.

We have discovered that certain specific baths of the general type described in our aforementioned pending application uniquely have several outstanding and unexpected properties. These baths, to be fully described below, have a markedly wider current density plating range, i.e., produce a bright deposit in the extremely deeply recessed areas, as well as allowing the plating to be carried out at higher current densities. Thus not only are the most complicated articles fully plated, but since the plating can be carried out at higher current densities, the actual plating time is significantly reduced. Moreover, the sulfide compound used is of such a stable nature that up to 1.0 gram per liter and above can be used without formation of harmful breakdown products. In other words, the concentration of the specific sulfide component of this invention is not critical as is the case with sulfide compounds in general.

The plating baths of this invention comprise aqueous acidic copper plating baths containing dissolved therein 3,328,273 Patented June 27, 1967 a bath-soluble polyether compound containing at least 6 ether oxygen atoms and being free from alkyl chains having more than 6 carbon atoms together with from about 0.0005 to about 1.0 gram per liter of an organic polysulfide compound of the formula wherein R and R are the same or different and are alkylene groups containing 1-6 carbon atoms, X is hydrogen or SO H, and n is an integer of 2-5 inclusive.

The sulfide compounds of the invention are aliphatic polysulfides wherein at least two divalent sulfur atoms are vicinal, and wherein the molecule has one or two terminal sulfonic acid groups. The alkylene portion of the molecule may be substituted with groups such as methyl, ethyl, chloro, bromo, ethoxy, hydroxy etc., but preferably R and R are unsubstituted polymethylene groups containing 3 carbon atoms. The various sulfonic compounds may be added to the plating baths as the free acid or the alkali metal salts or the organic amine salts etc. Generally, it is preferred to use the free acids. Ex amples of some of the preferred polysulfide compounds of the invention are shown in Table I.

TABLE I.ORGANIC POLYSULFIDE COMPOUNDS The sulfide compounds of the invention are known compounds and may be prepared by any of several well known techniques. For example, compound 4 in the above table may be prepared by reaction of sodium sulfide with propane sultone at about F. to obtain mercaptopropane sulfonic acid, which is then oxidized With H 0 to obtain the disulfide.

The organic sulfide compounds illustrated in Table I when used alone in copper plating baths do not produce adequate brightness. However, when used in combination with from about 0.01 to 5 grams per liter of the hereinafter described bath soluble polyether compounds, full bright, ductile deposits are obtained over an extremely wide current density range. The bath can be operated at a higher current density than is possible using seemingly similar sulfides which are not polysulfides of this invention. Moreover, if the same amount of polyether were used by itself, a somewhat dull irregular deposit is obtained.

A second outstanding benefit of the baths of this invention is that the aliphatic polysulfides can be used at concentrations of more than 1 gram per liter without the formation of harmful breakdown deposits which otherwise tend to reduce brightness, especially in the low current density area. When using other sulfide compounds not of the invention, their concentration must be quite limited in order to avoid the formation of detrimental breakdown products.

It has been found that the organic polysulfide compounds of Table I when used in concentrations of 0.0005 to about 1.0 gram/liter, prevent the harmful striations and ribbing effects that polyethers such as polyethylene ethanols and glycols cause in the absence of at least 0.02 to 0.1 gram/ liter of chloride or bromide ion. By the use of the addition agents of the invention not only are the striations and ribbing effects eliminated without the need of chloride or bromide ions, but a very bright deposit is obtained. This is an unexpected result because with either material used alone in the bath, there is no indication of the remarkable enhancement of brightness which occurs when the two materials are used together. It will be appreciated that the elimination of the ribbing or striations effects is, in itself, an unexpected and important result, and this result is obtained with all of the compounds of Table I, though the matter of obtaining the highest brightness, not all of the compounds of Table I are equally effective.

The polyethers which are useful for the purposes of this invention, include polyether compounds containing at least 6 ether oxygen atoms and which are free from alkyl chains having more than 6 carbon atoms. It has been found that compounds containing alkyl chains of more than 6 carbon atoms tend to overfoam with air agitation.

In Table II are listed representative examples of the bath soluble polyether derivatives which can be used in combination with the compounds of Table I to give bright, ductile copper plate. The preferred compounds of Table II, from the standpoint of best cooperation with the compounds of Table I, to give smooth, striation-free, bright, ductile copper are the polypropylene propanols and glycols of average molecular weight of about 360 to about 1,000, i.e., polyethers which contain the group (C H O) where y is an integer of from 6 to about 20. Outstanding results are also obtained with polyethers containing the group (C H O) where x is an integer of at least 6.

It was further found that if low concentrations (0.001

to 0.05 gram/liter) of phenazine dye such as Janus Green B (see US. Patent 2,707,166) are used in conjunction with both of the above described additives of Table I and II, brightness and leveling is further improved and brilliant, high leveling, ductile copper plate is obtained over a still wider plating range. This type of brilliance and extremely wide bright plate range is not obtained when the Janus Green B is used just with the onganic sulfide compounds carrying sulfonic groups (the compounds of TableI), or when used just with the compounds of Table II. Also, the brilliance and ductility far exceed that obtained with Janus Green B type dyes used together with thiourea or such thiourea derivatives or acetyl or propionyl thioureas. (US. Patent 2,738,318, Mar. 13, 1956.)

The dyes of the phenazine class (the Safranine type) and more especially the phenazine azo dyes (the Janus Green B type) which make possible the greatly improved leveling and extended bright plating range can be represented by the following formula.

R is H, CH or C H D is H, CH C H OH, NH N(CH N(C H 80002115, SH, and N=NZ where Z:a coupling group, such as dimethyl aniline, aniline, phenylene diamine, and substituted anilines and phenylene diamines, naphthols and substituted naphthols, phenols and substituted phenols, thiazoles, benzothiazoles and aminobenzothiazoles, coupled to the azo linkage The preferred phenazine dyes are the Janus Green B type (Diethyl Safranine .Azo Dimethyl Aniline or Dimethyl Safranine Azo Dimethyl Aniline, C. 1. Nos. 11045, 11050), or the Janus Black R type, also C. I. 11975 (Colour Index, second edition, vol. 3, 1956-57), as these compounds make possible the highest leveling and the widest bright plate range.

The inorganic composition of the acid copper plating baths such as the acidic sulfate or acidic fluoborate may vary over rather wide limits. However, when very low acid contents are used, higher tank voltages are needed. In the examples listed below as illustrations of lustrous copper plating baths, the standard types of acidic copper sulfate and fluoborate baths are used for the inorganic composition. However, other acidic copper plating baths such as copper sulfonate, copper methane sulfonates, copper ethane sulfonates, copper propane sulfonates with excess acidity supplied by the free sulfonic acids, can be used with the combinations of additives of this invention to give highly lustrous plate.

Many inorganic cations which do not plate out from the normal acidic copper plating baths, may be present in concentrations as high as at least 25 grams/ liter without detrimental effects, for example, ferrous nickel, cobalt,

zinc and cadium cations. Chloride and/ or bromide anions should in general be kept below about 0.1 gram/ liter, and preferably at about 0.02 gram/liter. Air agitation or cathode-rod agitation, or solution agitation and cathode-rod agitation is desirable for highest speed plating and optimum results. The best bath temperatures are 25-30 C., though lower or higher (even up to 50 C. in some cases) temperatures can be used.

With the use of the combination of additives from Tables I and II and the combinations with the phenazine dyes, especially the Janus Green B types, it is preferred not to use surfaceactive agents, even though such anionic types as sodium octyl sulfate, sulfonated non-ionic types such as Triton 720 (U.S. Patent 2,489,538, Nov. 29, 1949), and similar materials, or polyoxy non-ionic wetting agents, have often been previously used in acidic copper plating baths with good results, they are not needed in the present type baths.

Below are some examples of a number of acid copper plating baths producing highly ductile, lustrous copper deposits over a wide current density range.

Example A Concentration grams/liter CuS0 .5I-I O 150-250 H 50 30-75 1,3-dioxolane polymer av. mol. wt. 5,000 0.05-0.15 (CH )-(CH SS(CH SO H 0.001-0.01

Temp. 20-50 C. Av. cathode current density 15 amps/sq. dm.

Example B CuBR, 150-225 HBF 10-30 H BO 0-30 1,3-dioxolane polymer av. mol. wt. 5,000 0.1-0.3 HO S(CH ).;S-S-S(CH SO H 0.001-0.02

Janus Green B 0.001-0.02 Temp. 20-50 C. Av. cathode current density, 15 amps./ sq. dm.

Example C CuSO .5H O 150-250 H 30-75 Polypropylene glycol, av. mol. wt. 350-750 0.05-0.2

HO S(CH SS(CH -SO H 0.001-002 Dimethyl Safranine azo dimethyl aniline 0.001-0.01 Temp. 20-50 C.

Av. cathode current density, 20 amps/sq. dm.

5 The addition agents of Tables I and II can be combined in the same molecule or combined with one the phenazine dyes, or they may be used as individual molecules as listed in Tables I and II mixed together in the same solution with or without the phenazine dyes because they 5 all deplete from the solution at very nearly the same rate. The compounds of Table I used in the very low concentrations of 0.0005 to about 0.025 .gram/ liter deplete practically exactly at the same rate as the phenaz-ine dyes used in the concentration range of 0.001 to 0.05 gram/liter.

TABLE II.POLY-ETHERS (Concentration range 0.01 to 5 grams/liter. The lower concentration for the higher molecular weight species) H c OBB-02114 2134) xoH z=5100 N SOaH l 0 a u(0CaHu);OH 1:4-10

r l 18 HO osnao CaHr-NOSO- What is claimed is:

1. A bath for electrodepositing ductile, lustrous copper comprising an aqueous acidic copper plating bath containing dissolved therein from about 0.01 to 5 grams per liter of a bath-soluble polyether compound containing at least 6 ether oxygen atoms and being free from alkyl chains having more than -6 carbon atoms together with from about 0.0005 to about 1.0 gram per liter of an organic sulfide compound of the formula:

wherein R and R are the same or different and are alkylene groups containing 1-6 carbon atoms, X is hydrogen or SO H, and n is an integer of 2-5 inclusive.

2. A bath as in claim 1 wherein R and R are polymethylene groups and X is SO H.

3. A bath as in claim 2 wherein said polyether contains the group (C H wherein y is an integer equal to from about 6 to 20.

4. A bath as in claim 1 wherein said organic sulfide is H0 S(C H S1S-'(CH SO H.

5. A bath as in claim 4 additionally containing a bath soluble phenazine dye.

6. A method for electrodepositing ductile, lustrous copper comprising the step of electrodepositing copper from an aqueous acid copper plating bath containing dissolved there-in from about 0.01 to 5 grams per liter of a bathsoluble polyether compound containing at least 6 ether oxygen atoms and being free from alkyl chains having more than 6 carbon atoms together with from about 0.0005 to about 1.0 gram perliter of an organic sulfide compound of the formula:

XR (S) R -SO H wherein R and R are the same or different and are alkylene groups containing 1-6 carbon atoms, X ishydrogen or SO H and n is an integer of 2-5 inclusive.

7. A method as claimed in claim 6, wherein R and R are polymethylene groups and X is -SO H.

8. A method as claimed in claim 7 wherein said polyether contains the group (C;,H O) wherein y is an inte-.

ger equal to about 6 to 20.

9. A method as claimed in claim 6 wherein said organic sulfide is HO S(CH S--S(CH -SO H. 10. A method as claimed in claim 9 wherein said bath additionally contains a soluble phenazine dye.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner. G. KAPLAN, Assistant Examiner. 

1. A BATH FOR ELECTRODEPOSTING DUCTILE, LUSTROUS COPPER COMPRISING AN AQUEOUS ACIDIC COPPER PLATING BATH CONTAINING DISSOLVED THEREIN FROM ABOUT 0.01 TO 5 GRAMS PER LITER OF A BATH SOLUBLE POLYETHER COMPOUND CONTAINING AT LEAST 6 ETHER OXYGEN ATOMS AND BEING FREE FROM ALKYL CHAINS HAVING MORE THAN 6 CARBON ATOMS TOGETHER WITH FROM ABOUT 0.0005 TO ABOUT 1.0 GRAM PER LITER OF AN ORGANIC SULFIDE COMPOUND OF THE FORMULA: 